DE3010945C2 - Method and apparatus for controlling exposure in a photographic copier - Google Patents

Description

The invention relates to a method for controlling the exposure in a photographic copier a translucent template and an image receiver with a light-sensitive layer are optically coupled to each other, the template by means of a movable point of light of a cathode ray tube via a « Optical imaging system on the image receiver v / ird imaged, wherein the scanning speed of the light point is variable, and the output signal of a photodetector, which on that of the cathode ray tube remote side of the image receiver is arranged to control the intensity and the scanning speed " speed or dwell time of the light point is used.

The invention also relates to a device for performing the method described above an image carrier for a light-sensitive image receiver, with an original carrier for a to be copied Original, with a device for imaging the original at the location of the image receiver, with a cathode ray tube for generating a punctiform scanning light beam for the original and the image receiver one responsive to the light beam modulated by differences in the optical density of the original Photodetector and with a control circuit acted upon by the output signal of the photodetector for controlling the intensity and the deflection speed or dwell time of the electron beam as a function of the optical density of the original.

With photographic copiers of the aforementioned type, transparencies or Prints are made. The purpose of the usual photographic copying process is to achieve the im Reproduce the original contained object as well as possible. However, there are also photographic 4 « Applications where perfect reproduction is not desired. Many scientific, military and topographical reproduction systems require the ability to modify the reproduction system in order to transfer all of the information available from the original to the reproduction material. The normal contrast and the normal tint cannot always be maintained, because for example, the ratio of the permeable cells between the blackest and the brightest point on the Origlnalphotographle 100: 1 or more, while the usual photographic copy paper only a light reflection ratio of approx. 20: 1 is generated.

Two basic types of cathode ray tube copiers are known: those in which the intensity of the light generated by the cathode ray is modulated and those in which the deflection speed of the scanning electron beam in the cathode ray tube is modulated.

In the case of intensity-modulated copiers with cathode ray tubes, the overall contrast of the reproduction changed in that the light let through by the transparency is changed within a given holiness range, which can be in the range from 2: 1 to 20: 1. Such copier machines often contain additional devices with which the contrast is optionally available within preselectable limits can be changed. In the case of the intensity-modulated devices, it is important that the deflection speed of the scanning beam should remain essentially constant, since the total exposure of each sub-area is equal to the product of intensity and time.

In speed-modulated copiers, however, the beam intensity is usually kept constant, since the scan speed is changed to take the contrast into account.

As most photocopiers with cathode ray tubes in the scientific or military field with high requirements are used. Precise control is required. It is therefore with every species of these copiers, attempts have been made to measure at least one component of the exposure, be it the scanning speed in the case of intensity-modulated devices or the beam intensity in the case of speed-modulated devices, to stabilize as much as possible.

In speed-modulated devices, the range of tones is generally sufficient compressed, but such devices do not lend themselves well to incorporating preselected contrast control.

From the prior art, for example, from US Pat Copier known. The speed modulation takes place in this according to the relationship

E = Κψ ~ Vs

> Here, E indicates the photographic exposure of the light-sensitive image receiver, Tn the local light permeability in the original that is to be reproduced, Vs the local speed of the scanning point on the exposure surface; K is a constant of proportionality, which includes, among other things, the light intensity of the projection point on the exposed surface and the number of times the point passes through the same point on the original.

i ^'1 according to this document, a geschwindlgkeitsmodullertes copying machine must always shorter exposure times have than a comparable copier with intensity modulation because the geschwlndigkeitsmodullerte unit continuously operates with an electron beam of maximum intensity in the cathode ray tube, while relatively a galvanically coupled, Intensltätsmoduliertes copying machine highest just at the point density the template reaches its maximum beam current in the cathode ray tube. However, this overlooks the fact that the maximum beam current in the case of intensity modulation can be four times or more greater than the maximum permissible beam current in a comparable speed-modulated device. It follows from this that, at maximum density, the exposure time with an intensity-modulated copier is shorter than with an equivalent speed-modulated apparatus. However, if an intensity-modulated copier operates with a maximum beam current of, for example, 1000 microamps and a sampling rate of, for example, 25.4 m / s, a speed-modulated copier should be able to provide the same performance.

Unfortunately, however, the persistence of phosphors has practical limitations; when using an actinically active luminescent screen of the type PIl In the cathode ray tube is the maximum sampling rate is limited to approx. 127 to 153 m / s, and even at these speeds you can -> unwanted edge and edge reinforcements arise in photographic reproduction. At a maximum scanning rate of a speed-modulated copier of 153 m / s and a contrast reduction in a contrast range of 100: 1, the minimum scanning rate must be 1.53 m / s. The experience has shown that a beam current of 100 microamps at a 'scanning speed of 1.53 m / s leads to at least a brown coloration of the phosphor and in the worst case, depending on the size of the light spot In the m cathode ray tube, d. H. depending on the current density of the beam, causes the phosphorus to be burned and of flakes off the fluorescent screen.

In an intensity-modulated copier according to US-PS 28 42 025 that is through the template and the Light falling from the image receiver is collected in a light collector 36, the resulting photodetector current

is amplified and fed to the grid 14 of a cathode ray tube so as to provide negative feedback cause by which the intensity of the light perceived by the photomultiplier is kept constant

There are a number of other publications in which intensity-modulated copiers are shown. In US-PS 37 00 329 it is said that the output of an improved rviaskensCnäiiüng a Deflection device (speed modulation) of the electron gun (intensity modulation) is fed.

In a photographic reproduction process and a device for carrying out this process, a cathode ray tube is used to generate a movable point of light which is caused by an optical Imaging system is mapped on the template. A first photodetector generates an output signal that is determined by the light that passes through the original and through the image receptor. That The output signal is amplified and, together with a reference signal, is used to control the intensity of the Cathode ray tube. Part of the imaging light is deflected and amplified onto a second photodetector and fed to a deflection circuit which determines the deflection speed of the cathode ray or the light spot. The first photodetector is in a closed control loop for the intensity of the light point. The second amplifier is also in an open control loop and has a function generator connected, in which dependent on the density distribution of the original comparison signals are generated.

The intensity and the deflection speed of the electron beam in the cathode ray tube can not can be changed independently of one another because of the afterglow at high deflection speeds of the phosphor of the cathode ray tube an incorrect exposure can occur, while at low deflection speeds with too high a beam current the phosphor can be destroyed.

In another known copier (US-PS 30 11 395), the residence time of the electron beam in the Cathode ray tube modulates, in which the light point is advanced step by step and point by point, wherein the dwell time is changed at each point to compensate for density differences in the original.

The object of the present invention is to provide a method and an apparatus for the same Exercise to indicate that incorrect exposures due to the afterglow of the phosphor of the cathode ray tube and destruction of the phosphor of the cathode ray tube under all copying conditions that occur can be safely avoided.

According to the method according to the invention, this object is achieved in that in a first area lower optical densities of the original with unchanged intensity of the light point with increasing optical density the scanning speed is reduced or the dwell time is increased, in a subsequent (> 5 second area with increasing optical density reduces the scanning speed or the dwell time increased and at the same time the intensity of the point of light increased and in a subsequent Another area of higher optical density with the intensity of the light point kept constant again Reduction of the scanning speed or increase of the dwell time takes place.

In the device according to the invention, this object is achieved in that the control circuit has a having the output signal of the photodetector applied to the current transformer, through which a first, to the Intensity control circuit and a second output current applied to the deflection or wavering control circuit can be generated, each of which represents the output signal of the photodetector, and that the Intensity control circuit current limiting means for setting upper and lower limit values of the first Having output current through which a range of the intensity of the electron beam is determined, in which the Intensity and the deflection speed or dwell time simultaneously in accordance with the change in the first uri the second output current can be changed, the intensities of the electron beam being kept constant outside this range.

Embodiments of the invention are shown in the figures and are explained below with reference to the hi Reference numerals explained and described in detail. It shows

Flg. 1 shows a block diagram to illustrate the relationships between the velocity and intensity modulation in a first embodiment of the device according to the invention for producing contact prints;

Flg. 2 shows a block diagram of a second exemplary embodiment of the device according to the invention for Making copies using the projection method;

Flg. 3 is a partially schematic block diagram of a third embodiment of the invention Device with a combined speed and intensity control circuit;

Flg. 4 is a partially schematic block diagram of a fourth embodiment of the invention Apparatus with a different embodiment of the combined intensity and speed control circuit;

Flg. 5 is a partially schematic block diagram of a fifth embodiment of the invention Apparatus with a combined intensity and waviness control circuit; and

Flg. 6 is a partially schematic block diagram of a contrast control for the intensity and speed or waviness control circuit of FIG. 4 or S.

It is known that the automatic control of the contrast in the copy by an electronic Contrast control via a cathode ray tube optimized for only one group of properties at best which is of the greatest importance for the particular application of the device in question. In general, the performance of each cathode ray tube used as a light source is determined by parameters such as the phosphor afterglow duration, the actinic performance, the contrast of the faceplate, aging and combustion of the phosphor, phosphor granules, irregular cells in the point size and related operating sizes 3 " limited. Furthermore, the application of cathode ray tubes as light sources has the use of lenses made necessary as light collimators and light collectors, creating another set of problems arises, which are connected to centrally arranged projection structures. In addition, the use of lenses creates other problems in terms of cost, size, etc.

An example of the limitation of the properties of the copier is the phosphor used for the fluorescent screens of the cathode ray tube. The actinic performance of type PII phosphors is roughly the highest of the many types registered and available; however, the decay time of a PH phosphor is typically approx. 35 microseconds to Ίΰ% and 250 microseconds to 1% of its maximum brightness, which is dependent on the radiation density of the electron beam. For results with optimal contrast, the scanning speed should not be higher than one dot diameter per decay period. In US-PS 29 21 512 a point diameter of 0.32 cm is proposed for practical purposes. This results in a maximum scanning speed between 12.7 m / s (decay to 1 «) and 91.5 m / s (decay to 10%). The contrast values are usually in the controllable range of an electronic copier with cathode ray tubes and electronic contrast control in a ratio of 100: 1. In the case of a speed-modulated device with maximum scanning speeds as defined above, the lowest deflection speeds are accordingly 0.127 m / s (decay to 1%) and 0.915 m / s (decay to 10%). In the case of a cathode ray tube with a beam current that is suitable for generating acceptable copying speeds and is, for example, 200 microamps, a scanning speed between 0.127 and 0.915 m / s can lead to aging and degradation of the phosphorus within minutes. . so

The above examples show that within the limits of practical photographic Exposure times in product-oriented photographic laboratories such as 10 seconds or less phosphors suitable for cathode ray tubes at high scanning speeds and afterglow problems exhibit aging and burn problems at low scan speeds, as well as intensity problems for actinic light with lower beam currents.

In the device described below, performances are achieved with regard to the exposure times that go beyond the performance of intensity-modulated or speed-modulated copiers. This is of critical importance for production-oriented photographic laboratories, because it achieves a comparatively higher throughput or the possibility of offsetting savings in the exposure time against other parameters. In this device, the exposure speed and the phosphor * o afterglow are coordinated with one another. Therein, an intensity control circuit varies the cathode current of the cathode ray tube over a range of intensity values in the ratio 4: 1, while the photodetector 20 generates a photocurrent which drops from 25 to 12.5 microamps. The product of this change gives the ratio 8: 1, corresponding to a density change of 0.9. In the following Table I theoretical changes in the photodetector current (/, „,), the cathode current U _K ) of the cathode ray tube and the scanning speed (in inches / s) are compared with changes in the density of the original; it is assumed that the brightness of the phosphor varies linearly with the beam current of the cathode ray tube.

Table I.

Changes in photodetector current, cathode ray tube beam current and scan speed as a function of the density of the original

density

Scanning speed (in / s)

0 50 0.1 39.7 .2 31.5 .3 25th .4 24.5 .5 23.5 .6 22.3 .7 20.8 .8th 19.3 .9 UJ 1.0 16 1.1 14.3 1.2 12.5 1.3 10 1.4 7.9 1.5 6.3 1.6 5.0 1.7 3.9 1.8 3.1 1.9 2.5 2.0 2.0 GM =
IM = Speed modulation
Intensity modulation

200 200 200 200 250 300 355 420 487 575 642 720 800 800 800 800 800 800 800 800 800

3000

2383

1893

1500 _i_

1470

1380

1335

1248

1158

1062

960

858

750 4_

600

474

378

300

238

189

150

120 J_

GM

IM / GM

GM

Table 2 shows theoretically the relationships between the density of the original and the changes in the Photodetector current with the scanning speed with constant beam current of the cathode ray tube In a typical speed modulated copier.

Table II

Density and photodetector current changes with scanning speed

density

Scanning speed (in / s)

0.1

.2

.3

.4

.5

.6

.7

.8th

.9

1.0

1.1

1.2

1.3

1.4

50

39.7

31.5

25th

20th

3000

2383

1893

1500

1200

949

750

600

474

378

300

238

189

150

120

continuation

Density Ι, _η , (μΛ) scanning speed (in / s)

1.5 158

1.6 125

1.7 1.0

1.8 .79

1.9 .63 2.0 .5

Table 3 theoretically shows the relationship between the density of the original and the beam current I _K at a constant scanning speed in a typical galvanically coupled, intensity-modulated copier.

Table III

Dense cells and pertinent fibers

density

0 8

0.1 10 ^2S

.2 12.7

.3 16

■ ^{4 20}

.5 25

.6 32

.7 40

.8 50 J ₅

.9 63.5

1.0 80

1.1 100

1.2 127

1.3 1

1.4 200

1.5 250

1.6 320

1.7 400

1.8 500

1.9 635

2.0 800 ^

Table IV shows a comparison of theoretical exposure times for the above three exposure systems on the basis of the reproduction of a template with graduated densities. The table shows a four times cheaper one Copy speed for copiers with combined intensity and speed modulation in the Compared to an intensity-modulated device and a 3.6-fold increase in copter speed in the Compared to a purely swiveling modulated copier. Table IV also shows the The fact that with high original densities the exposure times for intensity modulation are shorter than for Speed modulation means that with low original densities the exposure time for speed modulation are shorter than with the intensity modulation and that the combined intensity-speed- «> modulation not slower than any of the other modulation systems on their own, but more typically faster than this works.

Table IV

2.5 0.125 0.125 2.5 0.25 0.204 2.5 0.5 0.24 2.5 1.0 0.312 25th 2.0 0.5 2.5 4.0 1.0 2.5 8.0 2.0

Exposure times (s) at different densities with intensity modulation (IM),
Velocity modulation (GM) and combined intensity modulation speed _s (IGM)

Density in the GM IGM

¹⁰ 0.4

17.5 15.87 4.38

Conditions: 420 consecutive scan lines, each 12.7 cm in length and one line feed

from 0.031 cm to a 12.7 X 12.7 cm grid.

In a first embodiment of the device or of the copier according to FIG. 1, a cathode ray tube 1 is used to make a light-sensitive image receiver 18 made of photographic paper or

-5 to expose film. The exposure takes place through a photographic original 16, which can be a photographic negative. The combined control described below can be used in any irradiation device in which z. B. a laser or other energy beam is used, which in its intensity as well as its deflection speed or dwell time can be changed. The exposure takes place with a point beam of 0.32 cm diameter through a grid 13; the A point of light is focused on a transparent image and original carrier 15 by an imaging device or optics 14. The carrier 15 carries the original 16 and the image receiver 18 in mutual alignment to make a copy. To expose the image receiver 18, the cathode ray tube 1 generates a punctiform scanning light beam, which is shown in Flg. Designate 1 with 8 '! is. A photodetector in the form of a photomultiplier 20 is provided to measure the light passing through the image receiver 18 and to generate a photodetector current I _1n ,, corresponding to this light.

A second embodiment of the device is shown in FIG. The photodetector receives in it 20 that passed through the original 16 and the original support and from the image receiver 18 to the Image carrier IS 'reflected light. In all other respects, the operation is the same as in Flg. The device shown in FIG. 2 is identical to that of the device according to FIG. 1.

The device shown in Fig. 1 is a copier for making contact copies, in which the The negative and the print are kept in close contact, while the In Flg. 2 according to the arrangement shown the projection method works in which an image of the original 16 is generated and by means of the optics 14 on the Image receiver 18 is focused, which is supported by a carrier 15 'aligned in the usual way. Although in Flg. 2 only the measurement of reflected light is shown for the photodetector ItO, so is it possible to use a transparent support 15 'and the photodetector 20 behind the image receiver 18 to arrange, or to use a radiation plate together with the optics 14 to split off part of the light beam for measurement purposes.

The copier shown in the block diagram of FIGS. 1 and 2 contains a current converter 23 with a circuit which _provides the first (xl * pml) and second (al _pml ) output in a predictable manner currents in dependence on the photodetector 20 received photodetector current I _p " generated. Welter below are used in connection with FIG. 3 and 4 explain two different such current transformers 23, 23a. An intensity control circuit 25 changes the intensity of the electron beam in accordance with the first output current (ctl * _pml ) emanating from the current converter 23 by changing the bias voltage at the cathode 3 of the cathode ray tube 1.

- "Control circuits for changing the scanning speed or dwell time of the electron beam 8 in accordance with the changes Iu the second output current (al _pml ) emanating from the current transformer 23 are described below in connection with FIGS. 3 and 4, the means for changing the dwell time in connection with FI g 5. Both the intensity of the point beam of light and its scanning speed or dwell time are changed according to the radiation intensity received by the photodetector 20.

The following is related to the third. In Flg.3 illustrated embodiment of the specific structure of the current converter 23 and the intensity control circuit 25 will be described in detail.

In Flg. 3 With 1 is a cathode ray tube, with 2 the associated supply unit, with 3 the cathode and with 4 the control grid for the cathode ray tube. These elements work together to Generation of an electron beam 8 with a deflection yoke 10 along a first axis quickly and with a deflection yoke 12 is slowly deflected magnetically along a second axis, whereby on the Faceplate of the cathode ray tube I a luminous grid 13 is generated. The light beam 17 is through an imaging device or OpHk 54 on a carrier 15 for a photographic negative or positive

transparent, the original 16, thrown on which a translucent photosensitive image receptor 18 in is in close contact.

A photodetector 20, usually a photomultiplier with a high-voltage supply 21, responds to the light passing through the image receiver 18 and generates a photodetector current I _pm , which is fed to a current converter 23. The photodetector current passes therethrough a resistor 70, which forms one of a pair of balanced resistors 70, 73, and is applied to a transistor QIA, which is one of a balanced pair of transistors QIA. QIB forms on a common carrier 71. The base of the transistor QIA is connected to a negative reference voltage which is supplied by a Zener diode 74 and a resistor 75. The second output current cd _{pm is} available at the output of the transistor Q1A with a value α between 0.990 and 0.998. A voltage V _{111 is applied} to a discharge amplifier 72, which results from the product of the photodetector current and the resistance value of the resistor 70, adding the emitter-base voltage at the transistor QIA and the reference voltage. This voltage is represented as V \ typically within 0.01 »of the voltage V _1n . The amplifier 72 is required so that a very low base current and practically no voltage deviation via the setting potentiometer 76 is obtained. In the case of the copier version described here in particular, the input currents should not exceed 50 nA at the highest operating temperature.

The voltage V * _ja lies across the resistor 73 and the emitter-base path of the transistor QIB at the output of the reference voltage generator. Since the two commercially available transistors QIA and QIB can be adjusted to voltage differences within 0.5 millivolts and the resistors 70 and 73 are adjusted within 1 *, a current I * _{pm is} generated by the voltage V \ that is practically the M PhoiGdetekiorstrorr. is equal to. The coefficient output current of the transistor QIB then becomes the first output current al * ^ ₁ , and is within 1 * equal to the second output current al _pml. Although, as previously indicated, the first and second output currents are balanced, it is only necessary that the two output currents be related to one another in a predictable manner, generally linearly, but also nonlinearly or discontinuously. The second output current al _pm is a unipolar current which forms the input current for a deflection control circuit 30, 35 in the axis of the rapid deflection or .Y-axis. An integrator circuit 35 therein consists of an integrating capacitor 36, a deflection yoke 10 in the axis of the rapid deflection, an operational amplifier 37 and a bleeder resistor 38 for the current of the deflection yoke 10.

The magnitude of the second output current aJ _pml causes the desired rate of change of the *> current at the deflection yoke 10, while the bleeder resistor 38 generates a voltage which is determined by the magnitude of the respective current independently of this rate of change. A switching device 40 effective in the axis of the rapid deflection or A 'axis responds to the voltage developing across the bleeder resistor 38; it is limited by edge controls 42, 44 for the left and right edges of the raster, and its output changes from the highest positive to the highest negative voltage or vice versa.

If the highest positive voltage is at the output of the switching device 40, a current reversal sound 30 of the deflection control circuit 30, 35 works like a known "current mirror" (see for example the application information ICAN / 6668 from RCA, September 1974) and generates a current ac'l ' _pm , since the diode 33 is switched on and the transistors 28, 29 and resistors 31, 32 are balanced.

Conversely, if the greatest negative voltage is present at the output of the switching device 40, then the diode -to 33 blocks and the transistors 28, 29 are also blocked. The second output current cd _pm from the current converter 23 then forces passage through the diode 27 and via the base-collector path of the transistor 29. Depending on the type of voltage at the output of the switching device 40, the current reversing circuit 30 therefore generates a positive or negative directed electron flow, which is integrated in the deflection device 35 accordingly.

The sequence of switching states in the speed modulation in the copier described here is such that to the extent that light from the grid 13 falls on the original 16 in the area of low density, the photodetector 20 generates a high photodetector current I _pm , which over the Current converter 30 is output as a high second output current al pml and is output via the current _{reversing circuit} 30 with high values for al _pmt or a'l ' _pm , to the integrator circuit 35 acting in the axis of the rapid deflection ", so that at the deflection yoke 10 a strong current change occurs and the electron beam 8 is deflected at high speed. Conversely, if the light beam emanating from the grid 13 falls on an area of high density of the original 16, a low photodetector current I _pm occurs at the photodetector 20, which results in a low rate of change of the current im Deflection yoke 10 results, so that the electron beam 8 is deflected at a low speed earth.

In addition to its other functions, the switching device 40, which is effective in the axis of rapid deflection, has an output line 45 which leads to a dimming circuit 60 for the cathode ray tube 1 leads. By this masking circuit 60, the electron beam 8 of the cathode ray tube 1 is on the Line 63 at the left and right turning points of the determined by the edge control 42, 44 Grid hidden. This extends the life of the phosphor in the cathode ray tube 1 * o and its aging is reduced, resulting from a combination of maximum beam current and lower Scanning speed can result.

To change the exposure time in accordance with the photosensitivity of the photosensitive material on the image receiver 18, a control circuit 48, 50 is provided for the overall exposure. These Control circuit 48, 50 has the effect that the extent of the incremental feed during the deflection in the direction t " of the K-axis is changed between successive scans in the direction of the A'-axis so that a Overlap of the scans is effected in the direction of the A'-axis. The degree of overlap then determines the effective overall exposure. By means of an index 49, a capacitance circuit in an integration

circuit 48 changed in the axis of slow deflection or K-axis. The integration circuit 48 causes a forward and backward deflection of the electron beam 8 and thus contributes to the point-like arrangement of the electron beam 8 in the grid 13. Through the integrating circuit 48 in the axis of the slow deflection, in connection with its components, namely a step generator 46, the index control 49, a deflection yoke 12 in the direction of the axis of the slow deflection and a bleeder resistor 47, the number of the grid 13 forming Scanned lines controlled. A start-stop circuit of the control circuit 48, 50 for the total exposure 50 is switched on by the start switch 51 and determines the number of total exposures for producing each individual copy.
A switching device 56 with edge controls 55 and 57 effective in the axis of the slow deflection or K-axis determines the extent of the grid and results in a pulse count that is fed to the start-stop circuit 50 via a line 52, as well as a fade-out signal for the return , which is applied to the blanking circuit 60 for the cathode ray tube 1 via the line 61.

The galvanically coupled intensity control circuit 25 is controlled by the first output current al * _pmt , which is compared in the amplifier 82 with a fixed current / _3. The value of the fixed current is adjustable by current limiting means 78, 83 consisting of a potentiometer 83 and a limiting resistor 78 and is selected for the highest copying speed so that it is not greater than the highest first output current and not less than a fifth of this value. The highest photodetector current is 50 microamps and the fixed current I _{5 is} 25 microamps. At the output of the amplifier 82 there is a positive voltage of approximately 0.5 volts, and the diode 80 is switched on when the first output current is greater than / _s .

Preferably, the base of the transistor 86 is set by a voltage divider consisting of resistors 87 and 88 to such a high poSUäve voltage that a minimum current I _K of approx. 200 microamps flows at the cathode of the cathode ray tube, see Table I. the line 63, an isolating diode 84 and a limiting resistor 79 are applied to the inverting input of the amplifier 82 in order to set its output to a low positive voltage. In the event of a positive output signal at the masking circuit 60 conducts

~ Hence the transistor 89 and supplies the minimum current I _{11 to} the cathode 3 and the bias resistor 62, which is connected to the cathode bias voltage V _bb .

If the first output current td * _{pm is} equal to the fixed current / ,, the output voltage of the amplifier 82 reaches the value 0 and becomes negative for all values of the first output current below the fixed current, so that the beam current I _K increases. One. The beam current is limited by the maximum deflection of the

-W Voltage at the output of amplifier 82 on the negative side, but the photodetector current is attached Reaching this limit value depends on the value of resistor 81.

FIG. 4 shows a fourth exemplary embodiment of the copier in a partially schematic block diagram with simultaneous IntC-sity and speed modulation, in which the current transformer 23a, the Modulator 25a for the intensity and the current reversing circuit 30a the current converter 23, the intensity control circuit and the power supply circuit 30 of FIG. 3 replace.

As part of the current converter 23a, a field effect transistor of the P-channel enhancement type 94 causes a current to flow If through photon-coupled isolators 93, 92 and 91, which are commonly referred to as opto-couplers. The current flow / through the photon-emitting diode 93a produces a corresponding, but not generally or not necessarily the same current in the photodetector 936, which in this case is a

■ w represents a diode operated phototransistor. Since the current I, runs from the field effect transistor 94 ms through the series-connected opto-couplers 93, 92, 91, the respective phototransistors 936, 92 * and 916 will generate the same output currents within the scope of their adjustment. However, equality of these currents is not required, and the current generation can be linear, non-linear and also discontinuous.
The operating mode of the current transformer 23a is based on the P-channel enrichment and the high impedance

• is of field effect transistors from the An of the field effect transistor 94, so that when the transistor 94 and Absence of a current /, the phototransistor 936 is blocked and a high on the photodetector 20 Load resistance, usually above a few hundred megohms, is present. In conduction and power generation by the photodetector 20, the gate of the field effect transistor 94 necessarily takes a negative Voltage of a value that generates a drain current /, which, when the diode 93a is coupled to the pho'.on

5 "generates a shunt current flowing through the phototransistor 936, which is equal to the photodetector current I _rml . The value of the current _{I 1} is therefore correctly related to the photodetector current and replicates it correctly in the phototransistors 926 and 916 of the opto Coupler 92, 91, since the drain current I _{1 flows} through the series-connected photo-emitting diodes 93, 92a and 91a. Instead of the opto-couplers shown in FIG

by an outgoing from the photodetector 20 signal linear, non-linear or discontinuous iorhersagbarer in "manner is reacted so that thereby the power can be controlled as well as the deflection of the electron beam 8. In the cathode ray tube 1, both ^ss are used.

The current reversing circuit 30a works in conjunction with a rectifier bridge of signal diodes 95, 96, 97 and 98 with low leakage currents and short recovery times. Because of this rectifying

M 'effect, the switching device 40 acting in the axis of rapid deflection impresses its alternating voltage on the phototransistor 926 as a direct voltage, the collector of the phototransistor 926 always being positive with respect to its base. Just as the phototransistor 926 reproduces the photodetector current / ,, ", as current I ' _r ", the switching device 40 causes a positive or negative current Γ ρη, _{through the current reversing circuit} 30a, which only depends on the polarity of the output voltage the switchgear

<> 5 device 40 depends.

Similarly, the intensity control circuit 25a generates a current / ,, "" in the phototransistor 916, namely in that the drain current /, of the field effect transistor 94 through the opto-coupler 91 and the photo-emitting diode 91a flows. At maximum photodetector at low density of the original 16 is

also the current /, "" maximum and short-circuits the resistor 90 to the greatest extent. The voltage drop across the circuit consisting of the resistor 90, the phototransistor 916 and the resistor 87 is then the smallest. The base-emitter voltage across transistor 86 and the voltage across resistor 85 are therefore also minimal. Accordingly, the current supplied to the cathode 3 of the cathode ray tube via the resistor 85, the transistor 86 and the transistor 89 is also minimal. As the current I _pm generated in the phototransistor 916 decreases, the voltage drop across the resistors 90 and 87 and across the phototransistor 916 also increases, as does the current I _K and thus the beam current and the brightness across the cathode ray tube 1 The network of resistors 87, 88, 90 connected to the phototransistor 916 forms a current limiting means for generating an intensity control according to Tab. I.

In the further, in Fig. 5 partially shown schematically in the block diagram, the fifth embodiment. The device is a combined intensity and dwell time modulation for the electron beam 8 intended.

In US-PS 30 11 395 the modulation of the dwell time is described as a method for automatic contrast reduction; then a cathode ray tube is operated with constant intensity and constant luminous point size, the beam being faded out between the dwell times. At the dwell time modulus 5 lation, a light beam is used one after the other and step by step to illuminate a small area transparent template used, so that through this template in the contact or projection process Image receiver is exposed. During each exposure stage, the dwell time is proportional to the integral time of actinic light which passes through the original and causes exposure, and this light is through a photodetector like a photomultiplier measured. At the end of each dwell time, the directed ^ o Light beam directed onto an adjacent, previously unexposed part of the surface, on which the P ^ 'ichtung cycle repeated, and this process, is continued step by step until all surfaces of the publishers in the so are exposed in a controlled manner in a punctiform manner.

The photographic copier shown in Fig. 5 includes intensity and dwell control circuits 25a and 306, 35, 113, as well as additional circuits to control the point size and to hide the Electron beam between the dwell times, which are not shown because they are familiar to the person skilled in the art. In a typical device with a PIl phosphor, the maximum practical residence time on one is Beam current of 200 microamps approx. 1 ms. while with a copier with a contrast correction im Ratio 100: 1 the minimum dwell time is approx. 10 microseconds, which depends on the sharpness of the Focusing of the electron beam depends. With simultaneous intensity modulation and in compliance with the #> Limit values of 200 microamperes and for the product of beam current and time in waste disposal must then the maximum dwell time at a higher beam current such as 800 microamps to about 250 microseconds can be reduced to avoid aging or burning of the fluorescent screen.

In the In FIg. 5, the current transformer 23a and the intensity control circuit 25e remain unchanged compared to FIG. The opto-coupler 92 with the photo-emitting diode 92a and the phototransistor 926 is shown here as part of a control circuit 306, 35, 113 for the dwell tent. In detail, a current flows from the phototransistor 926 which, as previously described, is a function of a current / through the photo-emitting diode 92a. The opto-coupler 92 thus forms a means for charging a capacitor through this current I ₁ , which now forms a charging current for the integrating capacitor 110, at which it generates a voltage. The voltage takes effect at the amplifier 100 by being compared with a reference voltage which is derived from the opposites 111, 112 by a voltage divider. If the reference voltage is greater than the voltage on the capacitor HO, then the output voltage on the amplifier 100 is negative and the diode 99 blocks. If, however, the capacitor voltage is greater than the reference voltage, the output voltage of the amplifier 100 assumes its highest positive value, whereby the diode 99 is opened and the voltage is applied to the line 106, via which this positive voltage is applied to the control inputs of an analog, double-sided Switch 103 with controlled switching elements 103a, 1036, 10Jc, 103 </ is applied. A resistor 105 is used to reduce the impedance of the control line, so that statistical fluctuations when blocking the diode 99 at the switching elements 103a, 1036 or 103c cannot be effectively grounded. The switch 103 thus forms a means for discharging the capacitor 110.? <>

When the voltage applied to the line 106 becomes positive, the switching element 103c closes, and the Capacitor UO begins to discharge through resistor 102. At the same time switch 1036 closes, whereby the resistor 101 is grounded and thus connected electrically in parallel with the resistor 112. the The reference voltage at the junction of the resistors J91., 111, 112 then assumes a new value, which is smaller than the capacitor voltage. As a result, the amplifier 100 maintains a positive polarity at its output while the capacitor 110 discharges. If the condenser voltage falls below the new value the reference voltage, the output voltage at the amplifier 100 assumes negative values, the diode 99 blocks, the voltage on the line 106 falls to the value 0, and the switching elements 103a and 1036 open. The reference voltage then returns to the original value and a new charge begins of capacitor 110. w

When the output voltage of the amplifier 100 is negative and when the line 106 is voltage-free due to the blocking diode 99, the switching element 103c is also open. The non-grounded switching element 103 "is therefore at positive voltage via the resistor 104, and the switching element 103a" is brought into the closed state by connecting the resistor 107 at its junction with inverting diodes 108, 109, which an integrator circuit 35 in the axis associated with rapid distraction, is grounded. , The current flowing through resistor 107 as previously described, depending on the *> i Ausgangspoicrltät of the active in the axis of the rapid deflection Schaltelntichtung 40, directed positive or negative. In any case, this current is diverted to earth and does not arrive as a negative current through the diode 108 or as a positive

Ver current through the diode 109. The integrator circuit 35 acting in the axis of rapid deflection is working then Iu in the known manner of a sample-and-hold integrator in its Halie function.

If the amplifier 100 generates a positive output voltage, as previously described, the switching element 103c is closed and the resistor 104 causes the control voltage at the switching element 103d > to drop to almost zero, so that the switching element 103o ¹ opens and the resistor 107 no longer connects with earth. At the same time, the positive or negative current through the resistor 107 must run through the diode 108 or 109, whereby the integrator circuit 35 is switched to deflection mode. This happens at the end of each dwell time and lasts only as long as the discharge time of the capacitor HO. After the capacitor 110 has been discharged and the output of the amplifier 100 has been reset to negative voltage

'"the switching element 103rf is closed again and the resistor 107 is again short-circuited to earth, see above that the integrator circuit 35 is now working in the hold mode again.

The effect of phosphorus afterglow is a complication in modulating the residence time as well for devices with intensity or speed modulation. In theory, the cathode ray tube 1 be faded out by means of a fade-out circuit after a curling time over a time interval, the

> ^s the decay time of phosphorus is the same. in order to expose the various partial areas of the original 16 and the image receiver 18 as precisely as possible. However, the relative proportion of the total exposure of the image receiver resulting from the afterglow of the phosphor then remains uncontrolled and is not partially controlled as in a system without masking, so that the accuracy of the photographic exposure turns out to be worse than better.

- ° The foregoing have been described in a number of circuits in connection with the reproduction of a photodetector current, without causing upper and lower limit values have been considered. The photographic effect of a reproduction of a photodetector current in a cathode ray tube with a light point 0.32 cm in diameter is to produce a luminous, fuzzy one. Mask by means of which the overall contrast of the image can be reduced to a very low value. As already In

^{: i} of US-PS 29 21,512 is executed. such representations are scientifically informative, but unsatisfactory in terms of images.

A luminous picture tube mask is first described in GB-PS 7 13 285 and US-PS 28 42 025 and in US-PS 34 00 632 derived mathematically. While the electronic contrast reduction using a fuzzy mask is taught in the first two publications, the calculations relate to a sharp mask

■ "> to correct the tint. It should be noted that the electronic contrast reduction is ultimately a reproduction process with distortion of the tint.

In order to determine the extent of the control of the overall contrast while an exposure is being carried out, it is possible to use a contrast control, as shown in FIG. 6, between the photodetector 20 and the input of the current transformer 23 or 23a. The photodetector 20 receives this through

- ¹ ? Differences in density in the original 16 changed light and generated an output current on the line 139, which is connected, among other things, to a high-impedance input of a buffer amplifier 129 with a low basic current. The photodetector current forces amplifier 129 to produce a negative output voltage which is shared between resistors 130, i3i for reduction. The caught Signa! is at the gate G of the field effect transistor 94 and generates a drain current / _; who is the photo-emitting

Diode 93o opens and switches phototransistor 936 in such a way that, as previously explained, it dissipates the photodetector current to earth.

While at the field effect transistor 94, the voltage applied to the gate is linear with the output current can be related, however, a root dependency is preferred. Since the opto-coupler 93 is a linear or nearly linear acting element, the output current of the phototransistor 936 is also

■ ^ linearly compared to the current /, the photon source and thus equal to the photodetector current. The tension on line 139 will therefore generally have the following form:

V ₀ = KV ₀₀ (K-

^{S ()} where: V _{0 is} the contrast control voltage on line 139; V _(lO the gate voltage of the field effect transistor 9 * at the point of the current drop; l _r ", the output current of the photodetector 20; k and K " ind scale factors that inter alia with the voltage division at the resistors 130, 131 and the current transfer ratio in the opto-coupler 93. In the preferred embodiment of the device with combined intensity and speed modulation

"or intensity and dwell time modulation, V _{D is} approx. 8 volts with a photodetector current of 50 microamps and 4.8 volts with a photodetector current of 2 microamps, with 50 microamps with a density of 0.0 and 2 microamps with a density of 2, 0 in template 16. Blocking amplifiers 115, 127 limit the voltage excursions of V ₀ on line 139 to values that are determined by the maximum and minimum photodetector currents, which are determined by density values of 0.0 and 2.0 in the just

"" reproduced template can be generated. The amplifier 115 receives via its non-inverting input the maximum voltage applied to the wiper of the potentiometer 117 and compares this with the voltage V ₀ on the line 139. If the voltage V _{D is} less negative than the maximum voltage, the output voltage of the amplifier is reached 115 its negative maximum value, but the blocking diode 114 prevents any reaction on the line 139 and the voltage V ₀ . However, if the voltage V _{0 exceeds} the

^M negative maximum value of the voltage, the output voltage of the amplifier 115 becomes positive relative thereto, so that the diode 114 becomes sufficiently conductive to dissipate any excess current which the voltage V _n on the line 139 by more than a few microvolts from the maximum voltage Enlarged on the wiper of the potentiometer 117.

Similarly, the amplifier 127 receives the voltage V _n on the line 139 and compares it with the minimum voltage at the wiper of the potentiometer 119. If the voltage V _{0 is more} negative than the minimum voltage, the output voltage of the amplifier 127 becomes positive, and the blocking diode 128 prevents this output from making itself felt on line 139. Falls, conversely, the photodetector current to a value below the predetermined minimum current, so that the voltage V _n below the minimum value of the rake ^s voltage falls, as it is set on the potentiometer 119, the output voltage is rekitiv negative, and causes the amplifier 127, that the Diode 128 conducts and generates a current 139 on the line which is equal to the set minimum value. While the maximum values and minimum values of the voltage, which are set at the potentiometers 117 and 119, are suitable for defining the limit values for the voltage V ₀ , they also represent end points for a resistance circuit 126 forming an adjustment potentiometer for the signal strength insofar as all Voltages available on the potentiometer wiper are within the limits defined by the maximum and minimum values of the voltage. In contrast to the control for the total irradiation by the integration circuit 48 and the start-stop circuit 50, by means of which the barking intensity is set according to the sensitivity of the image receiver 18, the resistance circuit 126 provides a fine control for the exposure intensity as a function of the light transmission of the Original 16 scored.

The resistance circuit 126 for setting the directional strength is connected to the line 139 via an analog double-sided switch 132 with switching elements 132a to 132tf and via pairs of diodes 133 to 138. The control elements of the switch 132 are connected to a contrast selector switch 121 and also to noise dampening resistors 122 to 125. For example, the control line for switching b> element 132rfbei the contrast selector switch position zero connected to the resistor 122nd In this position of the contrast selector switch 121, the control line of the switching element 132c / via the line 130a is at ground potential V _DD and is therefore positive compared to the negative voltage V " on the line 131a of the switch 132. When the switching element MId is closed, the wiper of the potentiometer is the Resistance circuit 126 connected directly to line 139 and its associated points. According to the definition given earlier, the potentiometer carries a much larger current than the detector current and accordingly forms a low resistance. The voltage V _n on the line 139 therefore assumes the value of the voltage on the wiper of the potentiometer 126 and cannot respond to the photodetector current emanating from the photodetector 20. The setting zero on the contrast selector switch 121 therefore does not result in any reduction in contrast, regardless of the respective light intensity set on the resistance circuit 126.

When the contrast selector switch 121 is in position 1, the control line of the switching element 132c is at a relatively positive voltage compared to the negative voltage V _a on the line 131a of the switch 132. As a result, the switch 132c is closed and connects the line 139 via the push-pull switched diodes 135 and 136 with the wiper of the setting potentiometer forming the resistance circuit 126 for the exposure intensity. If the voltage V ₀ on the line 139 is within + or - 0.5 volts of the wiper voltage set on the potentiometer, the bias voltage on the diodes 135, 136 is inadequate for the line. Therefore, the line 139 is in this limited voltage range a voltage V ₀ which is generated solely by the photodetector current and does not otherwise affect; is. However, if the voltage V _{0 changes} to a greater extent, one of the diodes 135 or 136 becomes conductive and thereby limits the contrast reduction in the area of the selected exposure intensity. -w

In the positions 2 and 3 which can be set on the contrast selector switch 121, the switching elements iZlb or 132a are actuated accordingly and the other pairs of diodes 134, 37 or 133, 138 are switched on. With switch position 2, voltage deviations of + or - 1.0 volts are permitted on line 139, with switch division 3 of + or - 1.5 volts. As is shown further in FIG. 6, the analog switch 132 in the switch position 4 of the contrast selector switch 121 has no controlled switching elements which are switched on with a relatively positive voltage. There is then no connection between the potentiometer forming the resistor circuit 126 and the line 139 and the available contrast reduction is limited solely by the action of the amplifiers 115 and 127 in the manner previously described.

The use of diodes and the number of diodes used to control the overall contrast of the Photographic reproduction is just one way of using the circuitry of the preferred embodiment to realize the game. The person skilled in the art is familiar with other methods which are the same at this point Purpose can be used.

In addition 5 sheets of drawings

Claims (16)

Patent claims: 1. Method of controlling the exposure in a photographic copier, in which a translucent Original and an image receptor with a light-sensitive layer optically coupled to one another are, the template by means of a movable light point of a cathode ray tube via an optical Imaging system is imaged on the image receiver, the scanning speed of the light point is changeable, and the output signal of a photodetector, which is on the remote from the cathode ray tube Side of the image receiver is arranged to control the intensity and the scanning speed or dwell time of the light point is used, characterized in that in a first Area of low optical densities of the original with unchanged intensity of the light point with increasing optical density, the scanning speed is decreased or the dwell time is increased, all in one subsequent second area with increasing optical density, the scanning speed is reduced or the dwell time can be increased and at the same time the intensity of the light point can be increased, all in one adjoining area of higher optical density with again kept constant intensity of ! 5 light point, a further reduction in the scanning speed or an increase in the dwell time takes place. 2. Apparatus for practicing the method according to claim 1, with an image carrier for a photosensitive image receiver, with an original carrier for an original to be copied, with a device for mapping the original at the location of the image receiver, with a cathode ray tube for generating a point-like scanning light beam for the Original and the image receiver, with a photodetector that responds to the durrii differences in the optical density of the original and a control circuit to which the output signal of the photodetector is applied to control the intensity and the deflection speed or dwell time of the electron beam as a function of the optical density of the original, characterized in that the control circuit has a current transformer (23, 23a) to which the output signal of the photodetector (20) is applied, through which a first, on the intensity control circuit (25, 25a) applied and a second, on the deflection od he swell time control circuit (30, 35; 30a, 35; 30b, 35, 113) applied output current (<xl * _p ", and al _pm ) can be generated, each representing the output signal of the photodetector, and that the intensity control circuit (25, 25iO current limiting means (78, 83, 91 &, 87, 88, 90) for establishing upper and lower limit values of the first output current, by which a range of the intensity of the electron beam is determined in which the intention and the deflection speed or dwell time are simultaneously in accordance with the change in the first and second output current (al * _pml , <xl _pm ) are changeable, the intensities of the electron beam being kept constant outside this range. 3. Apparatus according to claim 2, characterized in that the current converter (23) has a pair of balanced transistors (QlA, QlB) for generating the first and second output current (acl * _pml , <xl _pm ) . 4. Device according to Ansf-uch 3, characterized in that the current transformer (23) has a pair of balanced resistors (70, 73) which are each assigned to one of the balanced transistors (QIA, QIB) . 5. Device according to one of claims 2 to 4, characterized in that the current limiting means are formed by a potentiometer (83) and a limiting resistor (78) which is connected to the wiper of the potentiometer (83) and that a current limiting mkxä through this the first output current (al * _pm ) opposite fixed current (/,) can be generated. 6. Apparatus according to claim 2, characterized in that the current transformer (23a) is a set of Having optocouplers (91, 92, 93). 7. Apparatus according to claim 6, characterized in that the current limiting means is a forest status network (87, 88, 90) having a phototransistor (92a) of the first intensity control circuit (25a) associated optocoupler (91) is connected. 8. Device according to one of claims 2 to 7, characterized in that the Abienksteuerschaltung (30, 35; 30a, 35) a switching device (40) for generating control signals for controlling a Has deflection yoke (10) for deflection in the X-axis and an integrator (35) on which the so second output current (al _pm ) is applied and by means of which the control signal generated by the switching device (40) and applied to the deflection yoke (10) can be changed. 9. Apparatus according to claim 6 or 7, characterized in that the dwell control circuit (306, 35, 113) a switching device (40) for generating control signals for controlling an in the axle the quick deflection of effective deflection yoke (10), as well as a loading and unloading device (92, 103) for a capacitor (110), by means of which the switching device (40) can be blocked step by step and Can be retained during the dwell time, the dwell time being controlled by the changes in the condenser (110) charging second output current (st / ,,,,,) is variable. 10. The device according to claim 9, characterized in that the duration of each residence time by the Rate of charge of the capacitor (110) in the dwell control circuit (306, 35, 113) and w> is determined by the second output current (<xl _pml ) emanating from the current transformer (23a). 11. Device according to one of claims 2 to 10, characterized in that a control circuit (48, 50) is provided for the overall exposure, which includes an integration circuit (48) for varying the deflection of the scanning light beam (17) in the X and V Direction and an index control (49), by means of which the step-by-step deflection of the scanning light beam in the V-direction can be controlled. <> 5 12. The apparatus according to claim 11, characterized in that the control circuit (48, 50) for the Overall exposure a switching device (56) for generating control signals for controlling the Includes deflection in the ^ -direction and that the integration circuit (48) one through the index circuit (49) has adjustable capacitance circuit, by means of which an overlap between successive Samples in the A "direction can be generated. 13. Device according to one of claims 2 to 12, characterized in that a fine control fCr the exposure is arranged between the photodetector (20) and the current converter (23a), which is a pair of blocking amplifiers for limiting the voltage excursions derived from the photodetector (20) and a resistance circuit (126) for selecting a voltage lying between the voltage excursions, by means of which the current supplied to the current transformer (22a) can be changed. 14. The device according to claim 13, characterized in that a control for the overall contrast there is provided the sine plurality of pairs of diodes (133-138) interposed between the photodetector (20) and the current transformer (23a) are arranged, are connected in series in push-pull and through the Blocking amplifier (115, 127) bridging a certain voltage source, and a switching device (121) has, by means of which a predetermined number can be selected from the pairs of diodes (133 to 138), to limit the power supply to the current transformer (23a). 15. Device according to one of claims 2 to 14, characterized in that the image receiver (18) is arranged on a master carrier (15) in close contact with the master (16). 16. Device according to one of claims 2 to 14, characterized in that separate carriers for the Template (16) and the image receiver (18) are provided and that between the template (16) and the Image receiver (18) an imaging device (14) is arranged.